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PERFORMANCE OF GREEN ROOFS IN TROPICAL CLIMATIC
CONDITIONS
••• _ •••• _ ••• • __ •• __ r
LIBRARY
UNIVERSITY OF MORATUWA. SRi LANKA
ICORATUWA
Shanika Nisansala Wijerathne
Thesis Submitted in partial fulfillment of the requirements for the
degree Master of Science
University of Moratuwa
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104529
Department of Civil Engineering
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, Sri Lanka '. ,
September 2012
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PERFORMANCE OF GREEN ROOFS IN TROPICAL CLIMATIC
CONDITIONS
.•.•. r: .•.----~-~
lIBRARY
UNIVERSITY OF MORATUWA, SRi LANKA
IIORATUWA
Shanika Nisansala Wijerathne
Thesis Submitted in partial fulfillment of the requirements for the
degree Master of Science
University of Moratuwa
1111111111111111111111111111111111111111
104529
Department of Civil Engineering
- ':'; L--University of Moratuwa C~') /1 I!
"
Sri Lanka - ..
September 2012
O,lf5~r;
104529
I'
Declaration
I declare that this is my own work and the thesis does not incorporate without
acknowledgement any material previously submitted for a Degree or Diploma in any
other University or institute for higher learning and to the best of my knowledge and
belief it does not contain any material previously published or written by another person
except where the acknowledgement is made in the text.
Also I hereby grant University of Moratuwa the non-exclusive right to reproduce and
distribute my thesis, in whole or in part in print, electronic or other medium. I retain the
right to use this content in whole or part in future works (Such as articles or other books)
Signatnre: ~ Date: ~/Plft()/2...
The above candidate has carried out research for the Master thesis under my supervision.
I'\t ----
Date: Po/OJ /;l-(I/L .Signature of Supervisor:
"
Abstract
Abstract
Growth ofthe world urbanization has been extensively accelerated since past few decades. With
the increasing urbanization, the land with permeable layers and moist have been altered. As a
result, urban heat island phenomenon has taken place, making the temperature in the cities to be
higher than the country sides. Heat island effect in cities is mainly because of non-natural heat
absorbing materials use in buildings and other man made structures. Natural greenery in the cities
was replaced by concrete yards and most of the cities urbanizing with more and more concrete.
Since there is no space to grow, adding greenery to cities is also an issue. Having greenery over
the roof or planting on roofs are now becoming popular in many countries. Green roofs playa
major role as a sustainable solution to minimize the heat island effect. This research discusses
about the effects on the surrounding temperatures, if the existing flat roofs in the Colombo city,
the capital of Sri Lanka, are replaced with green roofs. The reduction in the temperature in the
atmosphere was calculated using actual measurements on small scale models and computer
simulation. These findings were coupled with the energy balance of the city. From the results
obtained, it can be clearly shown that there's a significant reduction in the temperatures, in the
city when compared to the prevailing condition. The forecasted condition proves that the
foreseeable problem of urban heat island effect with the future developments can be drastically
reduced with the introduction of green roofs.
Another problem the world is facing today is energy crisis. Because of that world is now
focusing on the sustainable cities. The contribution of the green roofs towards the energy cost
saving when it is implemented in the city level in the existing flat roof slabs is calculated. A
Derob modeling is done and the AlC loads are obtained for different roof types throughout the
year and with the actual roof areas obtained for the city the energy cost saving is calculated. The
energy cost saving obtained was 12%. However when it incorporates with the actual practice the
desires of the population also should be analyzed. Identifying the implementation possibilities of
the green roofs in the city also is vital to achieve these identified benefits in the future. This was
achieved through a detailed questionnaire survey. With questionnaire survey it was found that
the awareness of the green roofs is 56.8% and the willingness to spend for a green roof is less
than 20% than the existing cost for an asbestos roof.
Key Words: Heat island effect, green roofs, computer simulation, energy cost saving, implementation
possibilities.
"
Acknowledgement
Acknowledgement
The author is immensely grateful to the research supervisor, Dr. R.U.Halwatura of the
Department of Civil Engineering for his invaluable guidance and support throughout the research
period.
Author wishes to extend her sincere gratitude to SRC university grant foundation for funding the
research programme.
The support given by Prof.M.R.TJayasinghe (Head, Department Civil Engineering),
Dr.A.A.DJ.Perera(Head, Division of Construction Management) and by ProfJ.M.SJ.Bandara
(Research Coordinator, Department of Civil Engineering) is greatly appreciated.
Author greatly appreciates the supports by the technical officer Mr. S.P. Madanayake and Miss.
Kanthi Manathunge and all the other technical officers of the Department of Civil Engineering.
Finally, author extend her kind appreciation to all the staff of the Department of Civil
Engineering, all the non-academic staff of the Department of Civil Engineering and all people
who helped and encouraged her to complete this research successfully.
Page ii
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Contents
Contents
Abstract i
Acknowledgement ii
Contents iii
I . Introduction I
I.I General I
1.2 Objectives 2
1.3 The Methodology 2
1.4 The Main Findings 3
1.5 The arrangement of the report 4
2. Literature Review 6
2.1 General 6
2.2 Urbanization 6
2.2.1 World Trends 6
2.2.2 South Asian Trends 8
2.3 Problems with Urbanization 9
2.3.1 Urban Transportation 9
2.3.2 C02 Increase I 0
2.3.3 Urban Air Quality Related Health Risk I I
2.3.4 Temperature Increment 12
2.3.5 Urban Green Spaces 13
2.3.6 Energy Consumption 14
2.4 Congested Cities I6
2.4.1 Problems Caused with traffic congestion 17
2.4.2 Sri Lankan Cities 18
2.5 Thermal Comfort in tropical climate .........•........................................................................ 23
2.5.1 Tropical Wet. 23
2.5.2 Tropical Wet and Dry 24
2.5.3 Thermal Comfort 25
2.5.4 Climate in Sri Lanka 28
Page iii
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Contents
2.6 Rooftop Gardening 30
2.6.1 Understanding the option 31
2.6.2 Design ofa Green Roof. 33
2.6.3 Benefits of green roofs 36
2.6.4 Demand for Green Roofs 41
2.6.5 Green roof Cost Issues 42
2.7 Roofing Systems and Housing in Sri Lanka 43
2.7.1 Housing Units 43
2.8 Life Cycle Costing 46
2.8.1 Design Service Life 46
2.8.2 Inflation 46
2.8.3 Interest Rate 47
2.8.4 Inflation Rates in Sri Lanka 47
2.8.5 Life Cycle Costing and Whole Life Costing 48
2.8.6 Life Cost Analysis 48
2.8.7 Discount rates in Sri Lanka .49
2.9 Summary 49
3. Performance of Roofs on Urban Heat Island Effect 52
3.1 General 52
3.2 Area Chosen 53
3.3 Measuring Roof Areas 54
3.4 Theoretical Frame Work 55
3.5 Energy Store by Each Roof 57
3.6 The Results 59
3.7 Summary 62
4. Energy Cost Saving with the Implementation of Green Roofs 64
,
4.1 General 64
4.2 The DEROB Modeling 65
4.3 Analysis 66
4.3.1 Initial Installation Costs of Roofs 67
4.4 Life Cycle Cost Comparison with Different Land Recovery Percentages 70
Pageiv
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Contents
4.5 Summary 73
5. Questionnaire Survey 75
5.1 General 75
5.2 The Questionnaire 75
5.3 The Analysis of the Questionnaire 76
5.4 Summary 80
6. Enhancement of C02 in Cities with Green Roofs 81
6.1 General 81
6.2 Site Description 82
6.3 Theory 83
6.3.1 Pearson Correlation 83
6.3.2 Regression Analysis 85
6.3.3 Standard Deviation and Mean 85
6.4 Results and Discussion 87
6.5 Summary 91
7. Conclusion and Recommendation 92
7.1 Conclusion 92
7.2 Recommendation 93
7.3 Future Work 94
Page v
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Figures and Tables
Figure 2.I:South Asian Rural Population Distribution as a Percentage of Total Population as in World Bank Indicators 2011 8
Figure 2.2: South Asian Urban Population Distribution as a Percentage ofTotal Population World Bank Indicators 20 II 9
Figure 2.3: Urban Traffic Congestion 10
Figure 2.4: Carbon dioxide Emission in 2003 in the World (Inmaculada and Martinez-Zarzoso, 2004) 11
Figure 2.5:Sketch of an Urban Heat-Island Profile (http://www.epa.gov/heatisld/about/index.htm) 13
Figure 2.6: Average Floor Space per Person in Urban Settlement (Giovanni Sanesi, 2006) 14
Figure 2.7: Energy Consumption in Selected Asian 5 Cities (Bettencourt, 2007) 15
Figure 2.8: Traffic Con gestion (Federal High way Adm inistration 2008) 16
Figure 2.9: Population Rise and Rate of Growth in Sri Lanka ( Census, 200 I) 20
Figure 2.10: Population Density by District 2001 20
Figure 2.11: Population Distribution Change from 1981 to 200 I (Census 200 I) 21
Figure 2.12: Annual Ambient Concentration ofS02 and N02 in Colombo 1998-2003 23
Figure 2.13: Prevalence of Tropical Climatic Condition in the World (physicalgeography.net.) .24
Figure 2.14: Simplified Psychrometric Chart (P.W. Faire 1994) 27
Figure 2.15: Zoning Arrangement in Sri Lanka 29
Figure 2.16: A Showcase of Icelandic Treasures, Magnusson, 1987 30
Figure 2.17: Old Green Roofed House 30
Figure 2.18: Farmhouse in a historical park in Iceland .31
Figure 2.19: Extensive Green Roof System (Richard M. Daley, 2005) .32
Figure 2.20: Intensive Green Roof System (Richard M. Daley, 2005) .32
Figure 2.21: Green Roof System (Linda S. Velazquez, 2005) 34
Figure2.22:Representing Bio Diversity 40
Figure 2.23:Green Roofed Building 41
Figure 2.24: Sri Lanka Inflation Rate 48
Figure 2.25:Sri Lanka Interest Rates 49
Figure 3.1: Sample Area Chosen 53
Figure 3.2: Measured Slab Roof Areas are Shown 54
Figure 3.3 Simulation Scheme 55
Figure 3.4:Modeled Houses from Derob 57
Figure 3.5: Temperature variation in different roofs with time 58
Figure 3.6: Energy stored values for different roofs 59
Figure 3.7: Air temperature variation with time for two cases 60
Figure 3.8 Temperature variations with time in all three cases 60
Figure 3.9: Temperature variation with time compared to normal air temperature 61
Figure 3.11: Comparison of energy storing capacity of different roof types 62
Figure 4.1: The Models Done With DEROB Modeling 65
Figure 4.2: AlC Load values with months for two cases 66
Figure 4.3: AComparison ofNPV Value with No Land Recovery 71
Figure 4.4: Comparison ofNPV Value with 100% Land Recovery 72
Figure 4.5:Comparison ofNPV Value with 50% Land Recover 73
Figure 5.1: Percentage of Different Roof Types in Colombo Area 76
Figure 5.2 Variation of roof type with the level of income 77
Figure 5.3: Expected purpose of using asbestos sheets 78
Figure 5.4: Expected purpose of using Calicut Tiles 79
Figure 5.5: Expected purpose of using Flat Slabs 79
Figure 6.\: Google Earth Images of Bambalapitiya , 82
Figure 6.2: Google Earth Images of V iharamahadevi Park 82
Figure 6.3: Geometic Interpretation of Regression Analysis(A. Buda and AJarynowski, 20 I0) 83
Figure 6.4: Variation of C02 with time 86
Figure 6.5: Variation of Flux from the sun with time 88
Figure 6.6: The temperature variation with time 89
Figure 6.7: Regression Standardized Residual Histogram for Viharamahadevi Park 90
Page vi
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Figures and Tables
Tabe 2.1 : Population Distribution by Sector in 18 Districts 8
Table 2.2:0ccupied Housing Units and Intercensal Increase for 18 Districts in 1981 and 2001 (Department of Census and
statistics 200 I) .45
Table 3.1 Measured Roof Areas 54
Table 4.1 :Collected Data for Each Roof Type 69
Table 4.2:NPV Calculation values for different roof type 70
Table 4.3: Results Summary of the NPV Calculation 70
Table 5.1: Roof Type with the Income Level 77
Table 5.2: Percentage ofProblerns Occurred with the Installation 79
Table 6.1: Correlation Values 84
Table 0.2: Pearson Corelation Values 87
Table 0.3: Statistical analysis for the whole data set. 88
Page vii
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